What is it with IS on Pens?

These six shots were taken handheld, three with IS on (setting 1) and three with IS off on my E-P1 with 14-42 II.

I did not make a note of which were with IS and which were not (the EXIF data, on Aperture 3, does not tell me). More importantly, I cannot tell the difference at 100% enlargement on my MacBook. Does this mean the IS is not working, or what?